This dissertation presents several studies designed to probe the mental representations that physics experts and novices form when interacting with typical instructional materials, such as diagrams and problem statements. By using recognition tasks and a change detection task, the mental representations of experts and novices are studied in a more direct way than with tasks such as problem sorting or interviews. Results show that the experience and knowledge of physics experts influence the features of visual stimuli that they encode. However, a recognition task designed to probe physics experts' representations of physics problems revealed no evidence for the presence of physics principles. The final study in this dissertation used eye-tracking and a measure of cognitive load to determine that animating multimedia learning content can help to focus learners' attention towards relevant items on the screen and in some cases reduce cognitive load as well.